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Abstract

The objective of this study was to relate earthworm assemblage structure with three different soil use intensities, and to indentify the physical, chemical, and microbiological variables that are associated to the observed differences in earthworm assemblage structure between soils. Three soil uses were evaluated: 1- Fifty year old naturalized grasslands; 2- Cattle-grazing fields converted to feedlot within the two years before the start of this work, and 3- Fifty year old intensive agricultural fields. Three different sites for each soil use were evaluated from winter 2008 through summer 2011. Nine earthworm species were identified across all sampling sites. The sites shared five species: the native Microscolex dubius, and the introduced Aporrectodea caliginosa, A. rosea, Octalasion cyaneum, and O. lacteum, but they differed in their relative abundances according to the system. The results show that earthworm community structure is linked to and modulated by soil properties. Both, species abundance and diversity showed significant differences depending on soil use intensity. A PCA analysis showed that species composition is closely related to the environmental variability. The ratio of native to exotic species was significantly lower in the intensive agricultural system when compared to the other two, lower disturbance Systems. Microscolex dubius was shown to be related to the naturalized grasslands and it was associated to Ca, pH, Mechanical Resistance, and to respiration. Aporrectodea caliginosa was related to high K levels, low enzymatic activity, slightly low pH, and low Ca, and appeared related to the highly disturbed environment. Eukerria stagnalis and Aporrectodea rosea, commonly found un the cattle-grazing system, were related to high soil humidity, low pH, low Ca and low enzymatic activity. These results show that earthworm assamblages can be good descriptors of different soil use intensities. In particular, Microscolex dubius, Aporrectodea caliginosa, and Aporrectodea rosea, showed different temporal patterns and species associations, due to the changes in soil properties attributable tos oil use intensity.

Author Comment

Biological indicators of ecosystem state are of increasing use in aquatic ecosystems, but their development for terrestrial ecosystems lags somewhat behind. This manuscript addresses the important issue of assessing changes on earthworm assamblages in different agroecosystems. The work presented here provides information about earthworm assamblage structure being sensitive to the different uses of the same soil. Our data shows that, as soil use intensity has a strong effect on soil´s physical, chemical, and microbiological parameters, those parameters in turn, are related to earthworm species richness and abundance. In this way, our manuscript provides hard data supporting that earthworm assemblage structure is a good descriptor of the functioning of the edaphic environment. The data also shows that earthworm assamblage structure can be tracked in such a way so as to provide information for soil health monitoring over a wide range of anthropogenic intensities of soil use.

Supplemental Information

Dataset for Falco et al

Complete dataset of all samplings with details on agroecosystem, numbers of individuals collected from each earthworm species and genus and all physical, chemical and biological data related to all the analyses presented

Carlos E Coviella conceived and designed the experiments, performed the experiments, analyzed the data, wrote the paper, reviewed drafts of the paper, field work.

Funding

This work was partially funded by a Grant from the Ministry of Science and Technology of Argentina, Project PICT-02293-2006, a grant UBACyT number G074, and by the Universidad Nacional de Luján. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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